Reactive astrocytes mediate toxicity in iPSC derived dopaminergic neurons

Neuroinflammation is a hallmark of Parkinson's disease (PD), a progressive neurodegenerative disorder characterized by the accumulation of α-synuclein and the death of dopaminergic neurons in the substantia nigra. Mutations in GBA are a common risk factor for PD, which can lead to lipid metabolism dysfunction, autophagy/lysosomal dysregulation, as well as the disruption of other cellular functions. In this study, we investigated the impact of the GBA-N370S mutation and astrocytic reactivity on α-synuclein pathology and neurotoxicity. To investigate the impact of reactive astrocytes on Parkinson's disease pathology, we employed iPSC-derived midbrain astrocyte and dopaminergic neuron co-cultures from control and GBA-N370S donors, as well as primary mouse midbrain astrocyte cultures and transcriptomic assays to examine the response of astrocytes to Tumor Necrosis Factor-α (TNFα) and Interferon-γ (IFNγ). We show that upon inflammatory stimuli astrocytes become reactive, leading to extensive transcriptional changes. RNAseq and experimental validation revealed that calcium transport and homeostasis were severely dysregulated, and functional studies confirmed that GBA-N370S astrocytes exhibited increased calcium release when treated with cytokines. We further explored the impact of inflammation on astrocytic neurosupport in an iPSC-derived dopaminergic neuron and astrocyte co-culture model finding that combined treatment of TNFα, IFNγ and α-synuclein pre-formed fibrils (PFFs) led to neurotoxic effects, suggesting that TNFα and IFNγ-activated astrocytes mediate α-synuclein PFF toxicity. Taken together, these data provide evidence of reduced neurosupport in both control and GBA-N370S iPSC-derived midbrain astrocytes exposed to inflammatory cytokines, suggesting a role for reactive astrocytes in PD pathology.